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- In electronics, the dynatron oscillator, invented in 1918 by Albert Hull at General Electric, is an obsolete vacuum tube electronic oscillator circuit which uses a negative resistance characteristic in early tetrode vacuum tubes, caused by a process called secondary emission. It was the first negative resistance vacuum tube oscillator. The dynatron oscillator circuit was used to a limited extent as beat frequency oscillators (BFOs), and local oscillators in vacuum tube radio receivers as well as in scientific and test equipment from the 1920s to the 1940s but became obsolete around World War 2 due to the variability of secondary emission in tubes. Negative transconductance oscillators, such as the transitron oscillator invented by Cleto Brunetti in 1939, are similar negative resistance vacuum tube oscillator circuits which are based on negative transconductance (a fall in current through one grid electrode caused by an increase in voltage on a second grid) in a pentode or other multigrid vacuum tube. These replaced the dynatron circuit and were employed in vacuum tube electronic equipment through the 1970s. (en)
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- Dynatron vacuum tube signal generator, 1931. It covered the range 1.8 to 15 MHz. The circuit was used in signal generators due to its frequency stability, which was compared to crystal oscillators (en)
- An early tetrode, the RCA 24-A from 1929, showing on the lefthand side the negative resistance "kink" in the curves due to secondary emission. At a screen voltage VC2 of 90 V it has negative resistance between about Vp = 10 to 60 V. (en)
- The dynatron oscillator circuit was also used as the local oscillator in early vacuum tube superheterodyne radio receivers, such as this 1931 Crosley model 122 seven tube radio. (en)
- A modern tetrode, the 6P25. Due to a coating on the plate, there is very little secondary emission, so there is virtually no negative resistance region in the curves, making this tube unusable for dynatron operation. (en)
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- Plate current vs plate voltage curves for tetrodes: (en)
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- Dynatron signal generator 1931.jpg (en)
- Tetrode.png (en)
- Crosley 122 "Super Buddy Boy" radio receiver 1931.jpg (en)
- RCA 24-A screen grid tube anode characteristics.png (en)
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- In electronics, the dynatron oscillator, invented in 1918 by Albert Hull at General Electric, is an obsolete vacuum tube electronic oscillator circuit which uses a negative resistance characteristic in early tetrode vacuum tubes, caused by a process called secondary emission. It was the first negative resistance vacuum tube oscillator. The dynatron oscillator circuit was used to a limited extent as beat frequency oscillators (BFOs), and local oscillators in vacuum tube radio receivers as well as in scientific and test equipment from the 1920s to the 1940s but became obsolete around World War 2 due to the variability of secondary emission in tubes. (en)
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